1. Field of the Invention
The present invention generally relates to electrosurgical probes. More particularly, this invention relates to a cutting loop for an electrocautery probe, wherein the cross-section of the cutting loop is tailored to enhance the performance of the probe through attaining a balance between the mass and surface area of the loop, yielding an enhanced current distribution such that resection and coagulation can be performed simultaneously, rapidly and to a desired degree with the probe.
2. Description of the Prior Art
Electrosurgical resection is a procedure in which damaged, diseased or enlarged tissue is removed with an electrocautery probe. An example is transurethral resection of the prostate (TURP), in which prostate tissue is removed by means of an electrocautery probe (e.g., a cutting loop) that is passed through the urethra by means of a resectoscope. This procedure has served as the historical treatment of benign prostate hypertrophy (BPH), cancer and prostatitus. Another example is endometrial ablation, which is an electrosurgical alternative treatment to hysterectomy in women with menorrhagia (abnormal uterine bleeding). In this case, an electrosurgical probe is passed through the vagina by means of a hysteroscope.
As understood by those skilled in the art, ablation and resection are electrosurgical effects accomplished by applying a highly damped radio frequency (RF) current to the tissue through an electrosurgical probe. Such current has been found to cut and/or coagulate tissue depending on power and wave length combinations. The active tip of the electrosurgical probe is in direct view of the surgeon at all times through the telescope which is part of the resectoscope. Electrosurgical probes have been available for some time in a number of shapes and sizes. U.S. Pat. No. 4,917,082 to Grossi et al. illustrates a number of resectoscope electrode (probe) types such as coagulating electrodes, knife electrodes, punctate electrodes, and roller electrodes. Another probe known in the art is referred to as a resectoscope loop electrode, and is used for TURP and other procedures. As shown in FIG. 1, this type of electrode 10 consists of an electrically-conductive U-shaped wire loop 12 supported between a pair of electrically-conductive arms 13. Notably, the wire loop 12 has a round cross-section along its entire length. Electrodes of the type shown in FIG. 1 have been available from numerous surgical equipment companies for about thirty years.
Resectoscope loop electrodes of the type described above provide adequate tissue cutting characteristics and adequate cutting speed, but with little or no coagulation affect, thereby allowing operative and post operative bleeding. Operative bleeding requires the constant attention of the surgeon to coagulate bleeders in order to prevent excess blood loss. Addressing the operative bleeding problem can account for a majority of the time required for the entire operation, and may necessitate changing electrodes (e.g., from the loop electrode to a coagulating roller-type electrode) numerous times during the procedure to control blood loss. Surgeons may blend electrosurgical cutting and coagulating current in an attempt to enhance coagulation during cutting, but in doing so reduce the cutting efficiency of the electrode, increase operative time, and may affect patient safety. In these cases, medical professionals may elect to increase power from the electrosurgical generator to maintain acceptable performance and decrease operative time. This tactic increases the potential for electrical shock to both patient and surgeon, and may cause premature electrode failure.
More recently, an electrode disclosed in U.S. Pat. No. 5,569,244 to Hahnen, available under the name WEDGE LOOP from Microvasive, has been available for use in endometrial ablation and prostatic resection. Shown in cross-section in FIG. 2, Hahnen discloses a U-shaped cutting loop 112 that is said to vaporize and resect tissue 118 while at the same time coagulating the tissue 118 in the resected area to avoid operative and postoperative bleeding. As shown, the cutting loop 112 is substantially triangular in cross-section, having sharp edges 112A at the intersection of the intersecting surfaces. The edge 112A portrayed in FIG. 2 as making the incision is termed the proximal edge because of its proximity to the electrode and its operator. The term "proximal" can also be seen as relative to the cutting direction during the resection procedure, when the cutting loop 112 is drawn toward the operator such that the proximal edge defines a cutting plane generally parallel to the surface of the tissue 118. The flat surface opposite the proximal edge is termed the distal edge of the cutting loop 1 12. The terms "proximal edge" and "distal edge" will be used consistently hereinafter in accordance with their above-noted accepted definitions.
While the cutting loop 112 depicted in FIG. 2 is said to have increased surface area for providing increased coagulation during resection, its triangular shape 112 creates drag or resistance to passing of the loop 112 through tissue, as depicted in FIG. 2. In addition, the mass of the cutting loop 112 is relatively high, requiring more power for the resection procedure. The combination of increased power and the irregular shape of the cutting loop 112 can burn and char the tissue, creating a poor quality pathology chip 120 as shown in FIG. 2.
As a result of the above-noted performance deficiencies, the cutting loop 112 of Hahnen must be moved very slowly through tissue to achieve adequate performance, which increases operative time. Since operative time is limited to the maximum safe time that the patient can withstand anesthesia, trauma, etc., the slow performance of Hahnen's triangular-shaped cutting loop 112 limits the area of tissue that can be treated. In such cases, medical professionals may elect to increase power from the electrosurgical generator to maintain acceptable speed and performance in order to decrease operative time. As was noted previously with the prior art round cutting loop 12, increasing the power to the triangular cutting loop 112 increases the potential for electrical shock to both patient and surgeon, further decreases the quality of the pathology chip, and may cause premature electrode failure.
Thus, it would be desirable if an improved cutting loop for an electrocautery probe was available for performing electrosurgical resection procedures, wherein the cutting loop promoted the performance of the probe such that resection and coagulation can be performed simultaneously, rapidly and to a desired degree.